Systems which are provided with a burner adapted to combust a fuel/air mixture in a combustion chamber and having a recuperator or heat exchanger in which another fluid medium is heated by indirect heat exchange with the combustion gases from the combustion chamber before these gases are discharged, are commercially available in a varity of sizes and configurations and for many purposes.
For example, the principle described is used in boilers for the generation of hot water for home heating purposes or industrial purposes, in furnaces for the heating of air, e.g. in space heaters, for water heaters and, indeed, for practically any purpose in which a heated fluid is desired.
It is, however, difficult to balance the various factors which enter into the design of such heating installations. For example, for efficient heating of the fluid it is desirable to abstract heat from the combustion gases until these gases are reduced in temperature to below the dew point. This, however, can create significant corrosion problems because the combustion gases resulting from the burning of the fossil fuels usually contain acidic gases which are activated as the temperature drops below the dew point to produce corrosive acids.
On the other hand, if the heat exchange is effected so that the temperature is not reduced below the dew point, a portion of the sensible heat of the combustion gases and of the thermal energy generated by the combustion process may be lost.
Furthermore, commercial units of prior-art types are seldom compact or of such small size as to enable them to be conveniently used for home heating applications for the heating of domestic hot water supplies or the like with very high efficiencies.